Such a mooring system is generally known and examples thereof are described in report OTC 3567 "THE MOORING OF A TANKER TO A SINGLE POINT MOORING BY A RIGID YOKE" presented at the 11th annual OTC Conference in Houston, Apr. 30-May 3, 1979, especially FIGS. 3,5 and 6. Said known mooring systems are based on the principle that the connecting means, maintained under tensile stress by means of the buoyant body, exposed after a movement from the central position to a horizontal force component which increases as the deviation from the central position increases, and which is derived from the force upwardly exerted by means of the buoyant body on the connecting means. When the buoyant body is not completely submerged the deviation will furthermore result in an increased water displacement so that the upwardly directed force and therewith the horizontal return component increases. Said mooring systems are relatively simple and stable systems as a result of the mutual cooperation between the vessel, floating on the water surface, the rigid pivotable arm structure and the buoyant body. Said buoyant body may form a part of the connecting means, however it can also be a float which is firmly attached to the rigid pivotable arm structure.
Besides this known system there is also a still older system comprising a buoy having means for connecting a ship thereto, which buoy is kept in place by means of anchor chains extending in different directions in diverging relationship and attached to the sea bottom. Such a system is for instance illustrated in FIG. 2 of the above mentioned OTC 3567 report. This older system is based on the principle that after displacement of the buoy the weight of one or more of said chains generates a return force which in said respective chains is larger than the forces exerted on the buoy by the other chains, so that the buoy is brought back to the original central position.
In great depths problems arise. When one has to take into account heavy storms and great depths of a few hundred meters, then for anchoring said buoy by means of chains one has to use chains having a weight which will be out of all proportion and the handling of which becomes impossible.
If the system with a connecting means tensioned by means of buoyancy is used, then for greater depths one has to use bodies with a large buoyancy to have sufficient force to create a usable horizontal return component at a small deviation from the vertical position. That means however, that in the connecting means impermissible stresses can be developed, whereas in heavy weather conditions unacceptable situations can arise in which the connecting means is overloaded and there is a risk that the vessel may deviate too far from the desired position without being sufficiently returned.
An object of the invention is to offer a solution for said problem.